Apparatus to improve resolution in a scanned transparancy system

ABSTRACT

Apparatus to improve resolution and decrease distortion in system wherein a video signal is obtained by scanning a transparancy in a manner which requires increased scan speeds as the scanning spot moves away from the center is shown. A radial distortion lens having high axial demagnification decreasing toward the edges is placed between the scanner and transparancy and means are provided to correct the scan so that the combined output of the scanner and lens is the same as the scanner alone, the combined system resulting in a smaller spot size on axis and a decrease in required scanning speed toward the edges.

Friedman [54] APPARATUS TO IMPROVE RESOLUTION IN A SCANNED TRANSPARANCYSYSTEM [75] Inventor: David Friedman, Framingham,

Mass.

[73] Assignee: Singer-General Precision, Inc., Binghamton, NY.

[22] Filed: June 1, 1971 [21] Appl. No.: 148,838

[52] U.S. Cl. ..178/7.7, 315/27 GD [51] Int. Cl. ..l-l04n 3/16 [58]Field of Search ..l78/6.5, 7.7, DIG. 28

[56] References Cited UNITED STATES PATENTS 3,511,928 5/1970 Ratliff,Jr. ..l78/6.5

Primary Examiner-Robert L. Richardson Assistant Examiner-Donald E. StoutAtt0mey-Francis L. Masselle, John C. Altmiller and William Grobman [57]ABSTRACT Apparatus to improve resolution and decrease distor- I 3Claims, 3 Drawing Figures X M H Xi T FSS u 0 Scan 1 Y 1 37 Y LDeflection Computer Mun. V

33 35 43 4| 39 Square F? PATENTEDFEB 1 31% 3,716,660

To FSS Deflecfion v INVENTOR.

AGENT APPARATUS TO IMPROVE RESOLUTION IN A SCANNED TRANSPARANCY SYSTEMThis invention relates to visual and radar display systems for trainingpurposes which utilize scanned transparencies, and more particularly toapparatus for improving resolution in such systems.

Visual and radar display systems which display an image generated byscanning, with a flying spot scanner, one or more transparencies, havingrecorded thereon information relating to the portion of the earthssurface to be displayed, have been found to be very useful in aircraftsimulators. In the visual system two transparencies, one containing anorthophoto of a section of the earths surface, and the other coded withelevation data for the same section are used. In the radar system thesecond transparency contains radar reflectance information. Withmodification the same principles may also be used for a collisionavoidance radar training system. A detailed explanation of the type ofvisual system referred to is contained in U.S. Pat. No. 3,439,105granted to W. C. Ebeling et al. on Apr. 15, 1969 and also in US. Pat.No. 3,060,596 granted to A. R. Tucker et al. on Oct. 30, 1962.

In such a system, the information is recorded as an orthophoto and mustbe scanned to produce a display as would be seen by an observer. As theobserver views points further and further away, the speed at which thescan must move increases greatly until the horizon is reached.Theoretically the horizon is at infinity and spot speed likewise wouldhave to reach that speed. But an artificial horizon limit is set toavoid that problem.

If the spot cannot move as fast as required, distortion will occur atthe horizon area and the proper perspective will not be maintained. Thepresent invention seeks to solve this problem by utilizing a radialdistortion lens which will optically increase spot speed.

It is the principle object of this invention to provide a system forimproving resolution and decreasing distortion in a scan transparencysystem.

It is also an object to provide such a system by using a radialdistortion lens between the scanner and the transparency along withshaping circuits to correct the scan signals to take into effect theradial distortion.

Another object is to provide such a system which may be used wherever ascanner is required to scan radially with increasing speed toward theedges.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the features of construction,combination of elements, and arrangement of parts, which will beexemplified in the construction hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the-inventionreference should be had to the following detailed description taken inconnection with the accompanying drawing, in which:

FIG. 1 is a diagram showing the relationship between points on a displayand the same points projected on the ground;

FIG. 2 is a schematic side view of the preferred embodiment of theoptical portion of the invention;

FIG. 3 is a block diagram of a preferred embodiment of the shapingcircuits to correct for the radial distortion effects.

In FIG. 1 the lines of sight 13 from an observation point 11 to variouspoints in the ground plane 15 are shown. Point 11 can be the viewpointof an observer and plane 17 the window through which he observes theground plane 15. It can be seen that for lines 13 having equal angularor linear increments at the window plane 17 (as do the illustratedlines) the ground intersection points become progressively more distantin a non-linear fashion.

If plane 15 is assumed to be the transparency containing ground planeinformation and plane 17 a display on which that information will bedisplayed to an observer, it can be seen that a spot scanning plane 15to pick up the required information, to be displayed linearly at plane17, must move faster and faster as it goes away from the nadir point 19.The maximum spot speed will be limited by the flying spot scanner tubeand electronics. As previously .mentioned, distortion due to inabilityto achieve the required speed will often occur before reaching thedesired horizon limit.

FIG. 2 shows a radial distortion lens 21 placed between the flying spotscanner 23 and transparency 25. Optics 27 and photomultiplier 29 collectthe information generated in a manner well known in the art. Thedistortion lens 21 will be of a type having high axial demagnificationwhich decreases toward the edge. This results in the spot being smallernear the lens aXis, thereby improving resolution, and in the effectivespot speed being increased as the spot scans toward the horizon.

The system described in the above referenced patents computs the X and Yspot position according to the equations contained therein, based on theassumption that the spot will map linearly on the transparency. With thelens 21 interposed between the scanner tube and the transparency, meansmust be provided to produce the required output, not from the scanneralone, but from the combined scanner tube and lens 21. The radialposition of the spot on the tube may be found from the equation R X Y,where X Y are the horizontal and vertical coordinate positions of thespot.

The radial distortion may be expressed by R out R in times a function ofR ({(RD, where R is the square of the radial position of the spot at thetransparency indicated by point 22 on FIG. 2, R is the square of theradial position on the scanner tube indicated by point 24 and f (R) isthe function of the distortion lens. As previously mentioned lens 21will have high axial demagnification which decreases toward the edge.f(R) will be the expression for the transfer function of the particularlens in use.

The X and Y output from the scan computer of the above referencedpatents will be directly related to the desired position on thetransparency. If these signals are provided to the scanner tube theresult after passing through the radial distortion lens will be a spotat an improper position. Thus, the X and Y signals must be changed to Xand Y signals, where X and Y are the required scanner tube coordinatesto obtain a spot at X and Y on the transparency after radial distortion.

Such a shaping circuit to change the X and Y signals is shown in FIG. 3.Scan computer 31 is the computer in the above referenced patents andprovides the X and Y position signals. The X and Y outputs are squaredby conventional circuitry indicated by blocks 33 and then summed bysumming means indicated by block 35. The X and Y signals are alsosupplied to multipliers 37 which have as outputs the actual deflectionsignals. These output signals are squared in blocks 39 and summed inblock 41.

The outputs X and Y must be such that the final lens output would be asif X and Y were being imaged directly. Since R is a linear function of Xand Y, multiplying X and Y by the same quantity will have the effect ofmultiplying R by that quantity. In block 43 the R is multiplied by f (R)to obtain W The R output is summed in amplifier 45 with l and R R 0, isthe R that comes from the X and Youtputs of computer 31 (correspondingto the R of point 22 on FIG. 2) and also the R which must appear on thetransparency (point 22 on FIG Z). R is the R necessary at the lens inputto get R out at the transparency. (corresponding to the R of point 24 onFIG 2) Thus, when the R from block is multiplied by f(R) it becomes R,,,R /R in out: or R out When it is summed with 11 and l in amplifier45, if the R from block 43 is not equal to the R from block 35, an errorsignal will result which will be provided to multipliers 37 to bring theX and Y" signals to values which will cause the R values to be equal. Byusing a common signal from amplifier 45 to process both X and Y any openloop multiplication errors are cancelled out by the feedback loop. 7

The blocks 35, 41 and 45 may be high frequency operational amplifiers ofthe type well known in the art. Multipliers 37 and squares 33 and 39 maybe high frequency multipliers, suitable commercial embodiments of whichare made by Analog Devices of Norwood, Mass. The block 43 whichmultiplies R by f(R) may be constructed using well known analogcomputing techniques such as those discussed in Electronic Analog andHybrid Computers by Korn and Korn (Mc- Graw Hill Book Company, 1954).

The function f(R) will be found from lens design data or measurement ofthe lens using well known ray trace methods to provide the neededinformation for constructing block 43.

Thus, a system utilizing a radial distortion lens and appropriate scancontrol circuits which may be used to compensate for the distortionsintroduced in a scanned transparency system to improve resolutions andreduce distortion has been shown.

Although a flying spot scanner and transparency have been describedabove, the invention may also be used in other configurations where ascanning device scanning radially must increase scanning speed towardthe edges. For example, a television camera might be arranged to scan aconventional photograph using the same basic principles described above.

What is claimed is:

1. la a system wherein video information is developed by radiallyscanning with a scanning device an image source in accordance with twoscanv signals, developed by a scan computer, which cause deflection fromthe center of the device along two mutually perpendicular axes andwherein the scan rate is required to increase as the scan position movesaway from the center, apparatus to improve resolution and decrease thescan speed required comprising;

a. a radial distortion lens having igh axial demagnification decreasingtoward the edges placed between the scanning device and the imagesource; and means to correct the scan signals to take into account thedistorting effects of said lens, said means comprising: Lmeans to squareeach of the two scan signals; 2. means to sum the two squared scansignals; 3. means to multiply each of said two scan signals by acorrection factor to obtain two corrected scan signals; means to squareeach of said two corrected scan signals; means to sum said two squaredcorrected scan signals; means to multiply said sum by the transfer function of said radial lens; and means to sum the said multiplied sum, thesum of said squared scan signals and one to obtain said correctionfactor.

2. The invention according to claim 1 wherein said image source is atransparency and said scanning device is a flying spot scanner.

3. The invention according to claim 1 wherein said summing means areoperational amplifiers and said multiplying and squaring means are highspeed analog multipliers.

* F i i

1. In a system wherein video information is developed by radiallyscanning with a scanning device an image source in accordance with twoscan signals, developed by a scan computer, which cause deflection fromthe center of the device along two mutually perpendicular axes andwherein the scan rate is required to increase as the scan position movesaway from the center, apparatus to improve resolution and decrease thescan speed required comprising: a. a radial distortion lens haviNg highaxial demagnification decreasing toward the edges placed between thescanning device and the image source; and b. means to correct the scansignals to take into account the distorting effects of said lens, saidmeans comprising:
 1. means to square each of the two scan signals; 2.means to sum the two squared scan signals;
 3. means to multiply each ofsaid two scan signals by a correction factor to obtain two correctedscan signals;
 4. means to square each of said two corrected scansignals;
 5. means to sum said two squared corrected scan signals; 6.means to multiply said sum by the transfer function of said radial lens;and
 7. means to sum the said multiplied sum, the sum of said squaredscan signals and one to obtain said correction factor.
 1. In a systemwherein video information is developed by radially scanning with ascanning device an image source in accordance with two scan signals,developed by a scan computer, which cause deflection from the center ofthe device along two mutually perpendicular axes and wherein the scanrate is required to increase as the scan position moves away from thecenter, apparatus to improve resolution and decrease the scan speedrequired comprising: a. a radial distortion lens haviNg high axialdemagnification decreasing toward the edges placed between the scanningdevice and the image source; and b. means to correct the scan signals totake into account the distorting effects of said lens, said meanscomprising:
 1. means to square each of the two scan signals;
 2. means tosum the two squared scan signals;
 2. The invention according to claim 1wherein said image source is a transparency and said scanning device isa flying spot scanner.
 4. means to square each of said two correctedscan signals;
 5. means to sum said two squared corrected scan signals;6. means to multiply said sum by the transfer function of said radiallens; and
 7. means to sum the said multiplied sum, the sum of saidsquared scan signals and one to obtain said correction factor.